iotests: add testing shim for script-style python tests

iotests: add testing shim for script-style python tests

Because the new-style python tests don't use the iotests.main() test
launcher, we don't turn on the debugger logging for these scripts
when invoked via ./check -d.

Refactor the launcher shim into new and old style shims so that they
share environmental configuration.

Two cleanup notes: debug was not actually used as a global, and there
was no reason to create a class in an inner scope just to achieve
default variables; we can simply create an instance of the runner with
the values we want instead.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190709232550.10724-14-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
(cherry picked from commit 456a2d5ac7641c7e75c76328a561b528a8607a8e)
*prereq for 1a37e31244/88d2aa533a
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>